Brannigan died between the afternoon of February 24, 2013 and the following morning - during a 17-hour lockdown period when officers had next to no contact with inmates.

Her cellmate Lauren Ironside broke down in tears as she recounted waking around 4am and seeing Brannigan slumped against the wall, her head between her legs.

The inquest examined whether Corrective Services NSW and Justice Health breached their duty of care by putting the convicted drug dealer in the unsupervised cell while she was on sanctions for drug infractions.

It looked at whether the addict, who'd had at least three previous overdoses in custody, was given adequate treatment.

Police allege Brannigan and Ironside held a "drug party" in their cell on that fatal night with heroin and prescription drugs.

An autopsy found fresh track marks on Brannigan's left hand, and officers discovered syringes hidden in a shampoo bottle inside the cell.

One of the key questions was whether Brannigan was already intoxicated during her final visit at the centre on the afternoon of February 24.

Her visitor, Director of Women in Prisoner Advocacy Network Kat Armstrong, described Brannigan as "all over the place", obviously on an opiate and perhaps prescription medication.

Ironside also said Brannigan was "off her face" all day on three Rivotril pills, used for epilepsy treatment.

But correctional officers on duty that day said Brannigan's behaviour was normal.

Doctor Judy Pearl from the Police Forensic Services Group said the levels of Rivotril in Brannigan's system were so low she couldn't have been under the influence when Ms Armstrong visited.

Dr Pearl said Brannigan had injected the heroin herself that night, a few hours before she died.

This left prison officers with little opportunity to save her.

Brannigan's family made submissions she should not have been left unmonitored for 17 hours.

They argued if there had been a policy to check on inmates during the lock-in, officers could have saved her life.